CMP0155

New in version 3.28.

C++ sources in targets with at least C++20 are scanned for imports when supported.

CMake 3.27 and below assume that C++ sources do not import modules. CMake 3.28 and above prefer to assume that C++ sources in targets using C++20 or higher might import modules, and must be scanned before compiling, unless explicitly disabled. This policy provides compatibility for projects that use C++20 or higher, without modules, that have not been updated to turn off scanning, e.g., via the CMAKE_CXX_SCAN_FOR_MODULES variable. See the cmake-cxxmodules(7) manual for more details on C++ module support.

The OLD behavior for this policy is to assume that C++ 20 and newer sources do not import modules. The NEW behavior for this policy is to assume that C++ 20 and newer files may import modules if the compiler understands how to scan for their dependencies, and need to be scanned.

This policy was introduced in CMake version 3.28. It may be set by cmake_policy() or cmake_minimum_required(). If it is not set, CMake does not warn, and uses OLD behavior.

Note

The OLD behavior of a policy is deprecated by definition and may be removed in a future version of CMake.